I use a below similar SQL UNION in Tableau as Custom SQL to fetch my data

Select * from Server 1 UNION

select * from Server 2 UNION

Select * from Server 3 UNION

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Select * from Server 10

When one the above listed server is shutdown for the day / week the entire query fails and not data is retrieved from the other servers. Any ways to ignore or pass this..

For example: if Server 2 is not reachable at the time of Tableau refresh then skip that particular line and go to getch the data from the next server. I would like to know if there is any way in Tableau end